Bearing detection system

ABSTRACT

A system for determining the bearing of aircraft traveling in formation with respect to a master aircraft leading the formation. The master aircraft has a transmitter located thereon while each craft in formation has at least a pair of spaced-apart receiver means located thereon. If the craft are helicopters, each receiver means of a pair of receiver means is located at the respective end of a rotary blade of the helicopter. If the craft do not have rotary blades the receiver means are stationarily located and successive pairs of receiver means are successively sampled so that with respect to the spaced receiver means the equivalent apparent rotation is achieved. At the time when the signals from the transmitter arrive at both receiver means of a pair of receiver means at the same instant of time it is known that a line from the transmitter to the midpoint of a line connecting the pair of receiver means is perpendicular to the line connecting the pair of receiver means and the bearing is determined.

United States Ptent 1 [111 3,778,835

Scharf Dec. 11, 1973 [54] BEARING DETECTION SYSTEM [57] ABSTRACT [75]Inventor: Gerson Scharf, Fairfax, Va. A system for determining thebearing of aircraft trav- 73 A C t S n C r eling in formation withrespect to a master aircraft Sslgnee' orpo a I leading the formation.The master aircraft has a transaramus mitter located thereon while eachcraft in formation [22] Filed: Apr. 20, 1971 has at least a pair ofspaced-apart receiver means located thereon. If the craft arehelicopters, each receiver means of a pair of receiver means is locatedat the respective end of a rotary blade of the helicopter.

[21] Appl. N0.: 135,611

[52] US. Cl 343/113 R, 343/113 DE If the craft do not have rotary bladesthe receiver [51] lint; Cl. G01s 3/46 means are stationarily located andsuccessive pairs of [58] Field of Search 343/113 R, 113 DE receivermeans are successively sampled so that with respect to the spacedreceiver means the equivalent [56] References Cited apparent rotation isachieved. At the time when the T D S T S PATENTS signals from thetransmitter arrive at both receiver 3,550,130 12/1970 Shaw 343/113 DEmeans recelver means at the Same f 2 296 041 9/1942 Luck t 343/117 R oftime it 1s known that a line from the transmitter to g: 7 7/1940 Luck343/117 R the midpoint of a line connecting the pair of receiver3,553,698 1/1971 Keller 343/113 R means is perpendicular to the lineconnecting the pair 3,298,027 1/1967 Stover 343/113 DE of receiver meansand the bearing is determined. 3,528,070 9/1970 Young 343/11 VB 7 e MPrimary Examiner-Benjamin A. Borchelt 4 Claims 5 Drawing FiguresAssistant ExaminerDenis H. McCabe AttorneyBeveridge & DeGrandi 23 26 I 1V 29 SAMPLER GATE AMBiGUITY s RESOLVER A (22 t COMP ss DELAY l 24 $1 00+900 9 :Q( GATE ENCODER RELATIVE SUBTRACT ABSOLUTE BEARING BEARING ANGLEANGLE OUTPUT OUTPUT RECEIVER MEANS I INVENTOR A R cEwER MEANS 2 GERSONSCHARF PAIENIEDIIEG I I I973 3Q 778,835

' sIITET 1 CF 2 R FORMATION I HELICOPTER F l G. I

MASTER TRANSMITTER HELICOPTER 23 K27 26 29 AMBIGUITY SAMPLER 28 GATE F.I RESOLVER DELAY G 20 25 I X2l 3 24 SHAFT O i90 O i90-9 GATE T ENCODERRELATIVE SUBTRACT ABSOLUTE BEARING BEARING ANGLE ANGLE OUTPUT OUTPUT J,REcEIvER NEANs I INVENTOR l RECEIVER NEANs 2 GERSON SCHARF BY Ema at 12aQM ATTORNEYS PATENTED DEC 1 1 I973 SHEET 2 BF 2 TRANSMITTER EPOCHcowsmucnorv 9| millisec LJ 500 1 sec FIG 5 SMALL TIME SLOT LEADER O 5 NME GD mm 0 Dn P N E0 8' c &- M w u, S R N Mm R R T [k D M HM m E D M ANW R P 5 l N l 88 W N I. ww R N R m 0 N 6 m 3 MS mw H N T A L R A T 0 2 0iNVENTOR msou SCHARF BY d, ye 4m;

ATTORNEYS BEARING DETECTION SYSTEM This invention relates to an improvedsystem for determining the bearing or direction of one vehicle withrespect to another vehicle. It is particularly applicable to thedetermination ofthe bearing of aircraft, such as, for instance,helicopters or airplanes, flying in formation. The bearing detectionsystem of the present invention may be incorporated into a full-scalestationkeeping system wherein signals representative of the altitude,range, and bearing of each aircraft flying in formation are transmittedto a master aircraft several times each second. It may also be utilizedin a collision avoidance system where it would be desirable to know thebearing between aircraft.

. It is therefore an object of the invention to provide an improvedbearing-detection system.

It is a further object to provide a bearing-detection system which canbe incorporated into a full-scale station-keeping system where therelative altitudes, ranges, and bearings, of aircraft flying information are determined.

Briefly, the above objects are accomplished by providing one aircraftwith a transmitter means and another aircraft with at least one pair ofspaced-apart receiver means. At some respective bearing of the twoaircraft the signals from the transmitter means will arrive at bothreceiver means of a pair of receiver means at the same instant of time.At the time that this occurs a line from the transmitter to the midpointof a line connecting the pair of spaced-apart receiver means will be theperpendicular bisector of the line connecting the receiver means. If theangle between the line connecting the pair of receivers, and a line in adirection of the heading of the aircraft is then determined, therelative bearing is known. The absolute bearing, if desired, can then bedetermined by determining the angle between the nose of the aircraft anda reference direction.

In one embodiment of the invention, utilizing helicopters, thespaced-apart receiver means are placed at the ends of the rotary bladeor rotary blades of the receiving helicopter. These rotary blades effectrelative rotation of the receiver means.

In another embodiment, the spaced-apart receiver means are located onthe aircraft in a stationary fashion and a sampling network is used toeffect relative rotation of the pairs of receiver means.

The above-mentioned features and objects of the invention will becomemore apparent by reference to the following description taken inconjunction with the accompanying'drawings, in which:

FIG. 1 represents an embodiment of the invention wherein the receivermeans are located on the opposite ends of a helicopter blade;

FIG. 2 represents the system used to compute the angle of bearing of thesystem shown in FIG. 1;

FIG. 3 represents an embodiment where the receivers are stationarilylocated in a circular configuration; and

FIGS. 4 and 5 represent time slots of the stationkeeping system in whichthe unique bearing detector may be employed.

FIG. 1 represents an embodiment of the invention where it is desired todetermine the bearing of formation helicopters A and B with respect tomaster helicopter C which is the leader of the formation. In a practicalembodiment there might be a great number of formation helicopters,perhaps or more, and in such a case it would be desired to know thebearing of each formation helicopter with respect to the masterhelicopter.

While the embodiment of FIG. 1 shows determining the bearing betweenhelicopters in a formation and a master helicopter, it is also withinthe scope of the invention to determine the position of aircraft information with respect to a stationary transmitting source. Thus, itmight be desirable to determine the bearing of helicopters in formationwith respect to a stationary master station located either on the groundor in space.

In the embodiment shown in FIG. 1, the receiver means are located at theends of a rotaty blade of a helicopter. This rotary blade is a means forrelatively rotating the receiver means about a common axis. Actually,the helicopter may have more than one blade in which case pairedreceiver means may be located at respective ends of each rotary blade.As a practical matter, the receiver means could be antennas with theactual radio receiver or receivers located elsewhere on the craft.However, it is also within the scope of the invention to provide actualradio receivers located at the blade ends.

In FIG. 1 it is desired to determine the bearing of formationhelicopters A and B with respect to master helicopter C. Masterhelicopter C has a transmitter means located on it which transmits radiopulses toward formation helicopters A and B. Line LS in FIG. 1 is a linefrom the transmitter of master helicopter C to a point on rotary blade 8which is midway between receiver means 1 and 2. The angle between theline LS and the helicopter blade 8 is the angle 7. It is apparent thatat some time during a 180 rotation of blade 8, line LS will becomeperpendicular to the direction of the blade. Thus, in FIG. I, helicopterblade 8 is shown in positions 1 and 2. Position 1 illustrates a time inthe rotation of the blade when the angle 7 is at a value not equal toHowever, as the blade moves in a clockwise direction from position 1 toposition 2, the angle 7 moves closer to 90 until at position 2, y isequal to 90 and the line LS is the perpendicular bisector of the rotaryblade 8. At this instant of time the pulses incident on receiver means 1and 2 will arrive at the same time. This is because at this timereceiver means 1 and 2 are at the same distance from the transmitter.Thus, if we can determine at this time the angle d), which is the anglebetween the rotary blade and the line in the direction of the heading ofthe helicopter, we can determine the relative bearing of the fonnationhelicopter with respect to the master helicopter. This relative bearingangle in this case is 90 4). We can further determine the absolutebearing angle by substracting from the relative bearing angle the anglethat the line in the direction of the heading of the craft makes withthe reference direction. This angle in FIG. 1 is the angle 0, and so inFIG. I the absolute bearing angle will be equal to 90 (I) 6. 9, ofcourse, can be determined by a standard direction sensor such as acompass or gyroscope. d), the angle between the rotor blade and thedirection of the heading of the helicopter can be determined by anystandard device used for determining the instantaneous position of arotating shaft, such as a magnetic or optical shaft encoder.

If the master helicopter, instead of being at the bearing shown in FIG.1, was located at a bearing displaced from the bearing shown in FIG. 1,the new line LS would also be the perpendicular bisector of blade 8 andthe same bearing reading would result. This ambiguity can be resolved bysampling the receiver means a fraction of a revolution after the timewhen the signals arrive simultaneously, and noting at this later time atwhich receiver means the signals arrive first. Thus, in the positionshown in FIG. 1, assuming clockwise rotation, a fraction of a secondafter the signals arrive at both receiver means simultaneously, receivermeans 2 will be closer to the transmitter than receiver means 1 andhence the signals will arrive at receiver means 2 before they arrive atreceiver means 1. Thus it is determined that the master helicopter is atthe bearing shown in FIG. 1. Conversely, if the master helicopter hadbeen displaced 180 from the bearing shown in FIG. 1 (to the left andabove helicopter A instead of to the right and below it) receiver means1 would receive thesignals first a fraction of a revolution after thesignals arrive simultaneously.

In FIG. 1 it is also desired to determine the bearing of formationhelicopter B with respect to the master helicopter. This is done in thesame way as described in conjunction with formation helicopter A.Formation helicopter B in FIG. 1 is pictured at an instant in time whenline LR, the line from the transmitter to the midpoint of rotor blade 9,is the perpendicular bisector of blade 9. At this time, if thecorresponding angles (b and are determined, the absolute bearing angle ais known.

FIG. 2 shows an electronic system for computing the bearings of thehelicopters shown in FIG. 1. The outputs of receiver means 1 and 2 areconnected to the inputs of coincidence gate 20. Gate produces outputsignals at outputs 24 and only when the input signals to the gate arecoincident, that is only when the pulse signals from the transmittersource arrive at receiver means 1 and 2 simultaneously. This would, ofcourse, correspond to a position of the helicopter blade when a linefrom the transmitter to the midpoint of a line connecting the tworeceiver means would be the perpendicular bisector of the latter line.Shaft encoder 21, as mentioned above, is a standard magnetic or opticalshaft encoder which is connected to the shaft of the helicopter bladeswhich continuously provides an indication of the rotary position of theblade with respect to the heading of the helicopter. Shaft encoder 21 isdesigned to provide an output signal to subtractor gate 31 only when itis activated by the signal on output 24 of gate 20. At the same timethat an output signal appears at output 24 of gate 20, one will alsoappear at output 25. The signal at output 25 will be delayed for a timeequivalent to a fraction of a revolution of the blade in delay network22. The output of delay. network 22 is fed into sampler 23 which samplesreceier means 1 and 2 a fraction of a revolution after the signals fromthe transmitter arrive at the receiver means simultaneously, todetermine whether the signals are arriving at receiver means 1 orreceiver means 2 first. The sampled outputs of receiver means 1 and 2are then fed into inputs 28 and 27, respectively, of gate 26. Gate 26 isa standard block within the skill of the ordinary person in the art,designed so that if the sampled outputs of receiver means 1 and 2indicate that the transmitter signals are arriving at receiver means 2first, gate 26 will have an output on line 27". Conversely, if thetransmitter signals are arriving at receiver means 1 first, an outputsignal will appear at 28'. If the output appears at 27', this indicates,assuming clockwise rotation of the blade, that the ambiguity is resolvedin favor of the bearing of the master helicopter shown in FIG. 1. On theother hand, if the output appears at 28' it would indicate that thebearing of the master helicopter would be 180 displaced from the bearingshown at FIG. 1.

Ambiguity resolver 29 is a signal generating unit designed to generate asignal representative of the angle or the angle -90. Assuming to be +90,for the combination shown in FIG. 1, unit 29 will generate a signalrepresentative of +90 when the output of gate 26 appears at 27' and asignal representative of 90 when the output of gate 26 appears at 28' ofgate 26. The output of ambiguity resolver 29 is fed into shaft encoder21 where it combines with a signal representative of the angle (b sensedby shaft encoder 21 to product a shaft encoder output of (11 3:90, whichoutput is representative of the relative bearing angle.

To determine the absolute bearing angle a signal representative of theangle 0, the angle between the heading of the aircraft and the referencedirection must be combined with the signal representative of therelative bearing angle. For the configuration shown in FIG. 1 this angleis subtractively combined with the relative bearing angle. Thus in FIG.2 compass 30 provides an electrical output signal proportional to theangle 6, which signal is subtractively combined with the output of shaftencoder 21 in subtractor gate 31 to provide a signal representative ofthe absolute bearing angle.

FIG. 3 shows an embodiment of the invention employed on aircraft nothaving rotary wings. It is to be noted that the embodiment of FIG. 3 isnot restricted to use with aircrat and could be used to determine thebearings of any moving vehicles such as ships or land vehicles. In theembodiment of FIG. 3 the receiver means are stationarily mounted on theaircraft bodies and corresponding pairs of receiver means are sampledseveral hundred times each minute to effect relative rotation. Thus, inFIG. 3, receiver pairs A-B, C-D, etc. are sequentially sampled to effectrelative rotation. FIG. 3 is pictured an instant time when the line fromthe transmitter is the perpendicular bisector of the line betweenreceiver means C and D and the transmitter signals arrive at receivers Cand D at the same time. There is a network in the aircraft which has init stored the angles between the line A-B, C-D, etc., and a line in thedirection of the heading of the aircraft. These angles correspond to theangle (1) in FIG. 1. To determine either the relative bearing angle orthe absolute bearing angle, an electronic network similar to the networkshown in FIG. 2 would be employed.

It is apparent that the accuracy of the stationary receiver systemincreases as more receiver means are added. Thus, the embodiment shownin FIG. 3 in which pairs of receivers are circularly positioned attainsthe effect of a true rotary wing as the number of receiver means isincreased to the point where there is a receiver means located at everyconceivable point on the periphery of the circle.

FIGS. 4 and 5 are useful in describing a complete station keeping systemwith which the novel bearing detector of the present invention may beused. In a formation in which there are N aircraft, each represented byS,, and the master or flight leader represented by M, it is requiredthat the aircraft be provided with sufficient information to determineat least several times each second (a) the range between S and M, (b)the altitude differential between S, and M, (c) the bearing between S,and M, and (d) the heading and drift angle of M, all within acceptableRMS air tolerances.

The time hierarchy for the station keeping system is partitioned intoepochs as shown in FIG. 4. Each epoch is partitioned into N-l short timeslots and one long time slot. Each aircraft 8,, S S etc. is assigned ashort time slot in which it transmits and receives altitude and rangeinformation to the master, and a long time slot in which the mastertransmits the radio pulse which is used to determine bearing in themanner explained in conjunction with FIGS. 1 to 3. Aircraft within aformation can be synchronized periodically by either the leader or byanother source, perhaps a ground master, or submaster, and thissynchronization may take place at the station keeping frequency or atanother fre quency.

Assuming a design capacity of 19 aircraft in a formation flight, anepoch would consist of 18 short time slots as shown in FIG. 4 of 500microseconds duration each and one long time slot of 91 milliseconds.The 100 millisecond epoch provides a data rate of per second.

During a typical small time slot as shown in FIG. 5, the aircraftassigned to that slot transmits its altitude by means of a series ofbinary digits corresponding to its altitude in feet and receives thealtitude of the master in like manner. The formation aircraft can beequipped with a device for computing the differential altitude of itselfwith respect to the master. This is followed by a range request,consisting of a unique series of perhaps 9 bits. Upon receipt of therange request, the master responds with a series of 9 bits to enable therequesting aircraft to obtain the total delay for two-way ranging plusfixed delay. Upon subtracting the fixed delay and dividing the remainderby two, the range between S,, and M is determined. The master then sendshis 91 millisecond pulse to determine bearing. During this 91milliseconds, the master can also transmit coded se quences indicativeof his heading and drift angle. Thus it is seen that ten times eachsecond, range, altitude and bearing information is transmitted betweeneach aircraft in formation and a master.

While I have described and illustrated the preferred embodiments of myinvention, I wish it to be understood that I do not intend to berestricted solely thereto, but that I do intend to cover allmodifications thereof which would be apparent to one skilled in the artand which come within the spirit and scope of my invention.

What is claimed is:

1. A system for determining the bearing of a rotary wing aircraft withrespect to a pulse-emitting signaltransmitting source, said aircrafthaving a pair of spaced-apart receiver means located symmetricallythereon, means for indicating a time when a line from the transmittingsource to the midpoint of a line connecting said pair of spaced-apartreceiver means is perpendicular to said line connecting said pair ofspacedapart receiver means, said means for indicating comprisingcoincidence gate means for indicating a time when said pulses from saidsignal transmitting source arrive at said pair of spaced-apart receivermeans at the same instant of time, means for providing a signal representative of the angle between said line from the transmitting sourceat said time and a reference direction, which signal is representativeofthe absolute bearing of said body with respect to said source, saidmeans for providing a signal including;

means for providing a second signal representative of the angle betweensaid line from the transmitting source at said time, and the directionof the heading of the body at said time,

means for providing a third signal representative of the angle betweenthe heading of the body at said time and said reference direction,

means for providing a fourth signal indicative of one of or -90, andmeans for combining said second, third and fourth signals to producesaid signal representative of the absolute bearing of said body withrespect to said source.

2. The system of claim 1, further including means for sampling theoutput signals of said pair of receiver means at a time after said timebut before the time when said transmitted pulses again arrive at saidpair of receiver means at the same instant of time, and means responsiveto said sampling means for selecting whether said means for providing afourth signal provides a signal indicative of +90 or a signal indicativeof 90.

3. The system of claim 1, wherein said coincidence gate means has twoinputs which are connected to the output signals of said pair ofreceiver means, said gate means being arranged to generate a coincidencesignal when the output pulses of said receiver means are coincident, andshaft encoder means for providing said second signal when activated bysaid coincidence signal.

4. The system of claim 1, wherein said transmitting source is located ona second moving vehicle.

1. A system for determining the bearing of a rotary wing aircraft withrespect to a pulse-emitting signal-transmitting source, said aircrafthaving a pair of spaced-apart receiver means located symmetricallythereon, means for indicating a time when a line from the transmittingsource to the midpoint of a line connecting said pair of spaced-apartreceiver means is perpendicular to said line connecting said pair ofspaced-apart receiver means, said means for indicating comprisingcoincidence gate means for indicating a time when said pulses from saidsignal transmitting source arrive at said pair of spaced-apart receivermeans at the same instant of time, means for providing a signalrepresentative of the angle between said line from the transmittingsource at said time and a reference direction, which signal isrepresentative of the absolute bearing of said body with respect to saidsource, said means for providing a signal including; means for providinga second signal representative of the angle between said line from thetransmitting source at said time, and the direction of the heading ofthe body at said time, means for providing a third signal representativeof the angle between the heading of thE body at said time and saidreference direction, means for providing a fourth signal indicative ofone of +90* or -90*, and means for combining said second, third andfourth signals to produce said signal representative of the absolutebearing of said body with respect to said source.
 2. The system of claim1, further including means for sampling the output signals of said pairof receiver means at a time after said time but before the time whensaid transmitted pulses again arrive at said pair of receiver means atthe same instant of time, and means responsive to said sampling meansfor selecting whether said means for providing a fourth signal providesa signal indicative of +90* or a signal indicative of -90*.
 3. Thesystem of claim 1, wherein said coincidence gate means has two inputswhich are connected to the output signals of said pair of receivermeans, said gate means being arranged to generate a coincidence signalwhen the output pulses of said receiver means are coincident, and shaftencoder means for providing said second signal when activated by saidcoincidence signal.
 4. The system of claim 1, wherein said transmittingsource is located on a second moving vehicle.